1. Field of the Invention
The present invention relates to a sintered product of aluminum nitride having excellent durability at high temperatures, a process for the preparation thereof, and a baking jig such as a setter using the same.
2. Description of Prior Art
In recent years, integrated circuits such as ICs and LSIs have been fabricated in a highly density integrated form to produce large outputs accompanied, however, by the occurrence of a problem in regard to radiation of heat of silicon semiconductor elements. Under such circumstances, attempts have been made to develop a sintered product of aluminum nitride (hereinafter referred to as AlN) from a conventional insulating substrate of alumina sintered product maintaining a high thermal conductivity, a large electric insulating property and excellent matching with silicon in terms of coefficient of thermal expansion. Moreover, AlN has further been known as non-oxidizing ceramics having excellent strength at high temperatures in addition to SiC and Si.sub.3 N.sub.4.
Such an AlN sintered product is usually obtained by adding a sintering assistant composed of an oxide of the Group 3a of periodic table such as Y.sub.2 O.sub.3 or an oxide of the Group 2a of periodic table such as CaO to the starting powder of AlN, followed by molding, and then baking the molded article in a nitrogen-containing atmosphere at a temperature of 1600.degree. to 2000.degree. C.
In baking non-oxidizing ceramics such as AlN, etc., furthermore, it has been demanded to provide a material that exhibits excellent heat resistance at high temperatures and that can be used as a baking jig such as a setter for holding the molded article during the baking, such that the sintered product will not undergo deformation such as warping or will not be stained. AlN sintered product and BN sintered product of high purity that can be used as baking jigs have been concretely described in Japanese Laid-Open Patent Publications Nos. 197367/1989, 70269/1987 and 233081/1988.
In fact, however, most of the heat resistant non-oxidizing ceramic sintered products do not contain sintering assistant from the standpoint of decreasing the effect to the molded article. Therefore, the sintered product itself has a low density and develops deformation when it is subjected to a temperature in excess of 1500.degree. C. for long periods of time, and is not suited for use as a baking jig that will be used repetitively.
Moreover, the AlN sintered product that will be used for a variety of electronic parts and semiconductor parts must not be warped or deformed, must not be stained when it is machined into a substrate, and must not be coasened on the surfaces thereof. However, the use of a conventional AlN sintered product of even a high purity is not enough for completely preventing the deformation, stains and coarsening on the surfaces, and the yield of product is not maintained.